Experimental study and validation of MARS code for CCFL in passive emergency core cooling system (PECCS) of public acceptable simple SMR (PASS) system

Abstract

KAIST has developed a public acceptable simple SMR (PASS) system that applies the safety-related design characteristics of high temperature gas-cooled reactors (HTGR) to a water-cooled reactor. There is a new innovative safety system for decay heat removal, a passive emergency core cooling system (PECCS), in PASS. Countercurrent flow limitation (CCFL) is the most influential phenomena appearing in PASS-PECCS. In order to understand the CCFL phenomena appearing in the PASS-PECCS, down- scaled experiments were conducted in air/water conditions. From experimental study, we found that water head in an upper tank enhances water penetration into a lower tank compared with no water head case and there is an optimal water head condition. For a full-scale simulation of the PASS system using the MARS code, we proposed a new methodology simulating the CCFL phenomena without CCFL correlations and validated the nodal methodology with the results of the down-scaled experiments.